A method for obtaining a pure mixture of salts of yttrium, barium, and copper is to spray dry an aqueous solution of the nitrates. This method is disclosed and claimed in U.S. Ser. No. 95,084, supra. and see CA Selects: Colloids (Applied Aspects), Issue 12, 1988, 108:208961V, disclosing spray drying an aqueous solution of Y, Ba, and Cu nitrates.
Spray drying the nitrates does indeed avoid introduction of impurities, preserves the stoichiometry of the starting ingredients, and provides ready anion burn-off, leaving the pure mixed Y-Ba-Cu oxides, homogeneous at the atomic level. All of these features are important in the conversion of the mixed nitrates to a superconductor. However, from the production viewpoint, spray drying the solution of mixed nitrates suffers a serious disadvantage in that the spray dried nitrate product is hygroscopic. The product begins to absorb atmospheric moisture as soon as it is removed from the dryer, and it will quickly clump and cake, and will not flow freely. In this form it is difficult to process further. Handling requires minimal ambient exposure, and storage and shipping requires immediate hermetic sealing.
My invention provides a non-hygroscopic spray dried product and therefore avoids the foregoing problems. My invention is in the nature of an improvement in the above described spray drying process in that I substitute a mixture of monocarboxylates for the stated nitrates, other conditions being substantially the same. These monocarboxylates are the formates, acetates, propionates, and butyrates, being those generally derivable from monocarboxylic acids of the formula RCOOH, where R is H or alkyl of 1-4 carbons. A suitable monocarboxylate concentration for spray drying is about 10-15%.